Report on Soufriere Hills (United Kingdom) — 26 October-1 November 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 26 October-1 November 2005
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2005. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 26 October-1 November 2005. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
Volcanic and seismic activity at Soufrière Hills remained at elevated levels during 21-28 October. On 26 October around 2400, a pyroclastic flow traveled ~2 km down the volcano's NE flank. The pyroclastic flow was confined to the Tar River Valley. During the report week, the lava dome continued to grow and incandescence was visible at night. The sulfur-dioxide flux averaged 420 metric tons per day (t/d), below the long-term eruption average of 500 t/d. The hydrogen-chloride to sulfur-dioxide ratio measured on 26 October was at 1.3. According to the Washington VAAC, a pilot reported observing a thin layer of ash at a height of ~2.4 km (8,000 ft) a.s.l. above St. Croix on 28 October at 1010.
Geologic Background. The complex, dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat. The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone. The volcano is flanked by Pleistocene complexes to the north and south. English's Crater, a 1-km-wide crater breached widely to the east by edifice collapse, was formed about 2000 years ago as a result of the youngest of several collapse events producing submarine debris-avalanche deposits. Block-and-ash flow and surge deposits associated with dome growth predominate in flank deposits, including those from an eruption that likely preceded the 1632 CE settlement of the island, allowing cultivation on recently devegetated land to near the summit. Non-eruptive seismic swarms occurred at 30-year intervals in the 20th century, but no historical eruptions were recorded until 1995. Long-term small-to-moderate ash eruptions beginning in that year were later accompanied by lava-dome growth and pyroclastic flows that forced evacuation of the southern half of the island and ultimately destroyed the capital city of Plymouth, causing major social and economic disruption.